1. Field of the Invention
The invention relates to a discontinuous position detecting device and a method of detecting a discontinuous position that detects an actual position at which data and time information recorded on a magnetic tape is discontinuous.
2. Description of the Related Art
It has become possible for a recording device to record video data and audio data on videotape over a long period, according to improvements in high-density recording and data compression. For example, there has been developed an optical disk recording system that writes a collection of video and audio data that has been separately recorded by a videocassette recorder (VCR) into an optical disk (DVD-R). Further, there has been developed an optical disk player that reproduces video and audio data optionally selected by a user out of an optical disk (DVD).
FIG. 6 is a schematic illustration of a memory structure of a videotape 11 storing video and audio data thereon. The videotape 11 has a memory structure composed of a plurality of video tracks 15, each video track 15 having a video area 12 that stores video data, an audio area 13 that stores sound data and a sub-code area 14 that stores various information on the videotape 11. Ordinarily, the sub-code area 14 stores date and time information indicative of a date and time of recording, and time code information indicative of a tape position used for editing. The date and time information and the time code information is stored on the videotape 11 in relation to the video data and the audio data. The recording device records the date and time information, by using its calendar/clock function, on the videotape 11. Accordingly, when the recording is performed continuously, the date and time information is stored continuously on the videotape 11. On the other hand, when the recording is performed discontinuously, the date and time information on the videotape 11 becomes discontinuous. As the date and time of recording is changed at a position where the recording is stopped and restarted (hereinafter referred to as a discontinuous position). The recording device records, as the time code information, a time code of recording that is continued from the time code of previous recording. Therefore, the time code information is stored in absolute time continuing throughout the videotape 11, and is ordinarily composed of information on hours, minutes, seconds and frame number.
By using such date and time information and time code information, a user can easily select his desired picture materials from the videotape. Herein, the term “picture material” refers to as a collection of video and audio data indicative of a series of images and sounds. Japanese Laid-Open Patent No. 8-161872 discloses a picture material detecting device that detects and cuts picture materials out of the videotape by using the above-mentioned discontinuous positions of the date and time information. FIG. 7 is a schematic illustration of discontinuous positions AB and BC between picture materials, A 16, B 17 and C 18 recorded on a videotape 11, by way of example. Herein, it is assumed that the picture material detecting device uses such discontinuous positions AB and BC to cut the picture material B 17 from the videotape 11. When the date and time information is monitored while reproducing the videotape 11 in a tape feed direction (indicated by an arrow in FIG. 7), there is detected the discontinuous position AB between the end of the picture material A-16 (1999 Aug. 27 10:32:20) and the start of the picture material B 17 (1999 Aug. 27 12:10:10). This discontinuous position AB corresponds to a start time code of the picture material B 17 (00:03:00;00). Further, there is detected the discontinuous position BC between the end of the picture material B 17 (1999 Aug. 27 12:11:20) and the start of the picture material C 18 (1999 Aug. 28 10:03:10). The discontinuous position BC corresponds to an end time code of the picture material B 17 (00:04:10;00). These start time code and end time code are used as picture material time code information for cutting the picture material B 17 from the videotape 11. The last two numbers of the time code represent the frame number, and there are included 30 frames (from 0 to 29) of images per second.
Conventionally, the discontinuous positions of the date and time information are detected in the manner explained above, while reproducing the videotape 11 at normal speed. This allows detecting the discontinuous positions precisely, but it takes as much time as an actual time period required for reproducing the videotape 11, thereby being inefficient and time-consuming.
In order to overcome such a drawback, the detection of discontinuous positions is performed while fast-forwarding the videotape 11 or reproducing the videotape 11 at fast speed. However, this discontinuous position detection raises other problems as described below. FIGS. 8A and 8B show a relationship between a tape feed speed and a tape head scanning trail of a tape head. As shown in FIG. 8A, when reproducing the videotape 11 at normal speed, a head scan vector 23A that is defined by a tape head rotating speed vector 21A and a tape feed speed vector 22A is on a video track 24, namely, the tape head scans one video track 24. On the other hand, as shown in FIG. 8B, when fast-forwarding the videotape 11 or reproducing the videotape 11 at fast speed, a head scan vector 23B that is defined by a tape head rotating speed vector 21B and a tape feed speed vector 22B is diagonally spread over a plurality of video tracks 24, that is, the tape head scans over the plurality of video tracks 24. It is because the tape head rotating speed is kept constant without being increased, though the tape feed speed is increased. As a result, some of the date and time information and the time code information that should be detected is often skipped, without being detected. Therefore, the actual discontinuous positions of the date and time information will not be detected precisely, while fast-forwarding the videotape 11 and reproducing the videotape 11 at fast speed. The detected discontinuous positions often include some errors. The following problem comes up when cutting the picture material out of the videotape. FIG. 9 schematically shows errors occurred in detecting the discontinuous positions of the date and time information. It is illustrated that actual discontinuous positions AB and BC are mistakenly detected as incorrect discontinuous positions A′B′ with detection errors. In a case where the picture material B is cut out of the videotape based on the incorrect discontinuous positions A′B′ and B′C′, in reality, a part of the picture material B is cut away, at the same time, a part of the picture material C that is adjacent to the picture material B is mixed into the picture material B.
In order to overcome the above-mentioned problem, there is proposed to roughly detect a discontinuous position of the date and time information while the videotape is fast-forwarded or reproduced at fast speed, to rewind the videotape, and then, to detect an actual discontinuous position while reproducing the videotape at normal speed. After detecting the actual discontinuous position, the videotape is again fast-forwarded or reproduced at fast speed to detect a next discontinuous position. However, in this method, the videotape has to be rewound many times, thereby requiring complicated procedures.